Semiconductor device

ABSTRACT

A semiconductor device includes a lead frame; a circuit board located on the lead frame; a power device that includes a switching element and is mounted on the circuit board via a bump located between the power device and the circuit board; and a heat releasing member connected to the power device. The circuit board may be a multi-layer wiring board. The circuit board may include a capacitor element, a resistor element, an inductor element, a diode element and a switching element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application that claims priority onU.S. application Ser. No. 14/620,854, filed Feb. 12, 2015, which isbased upon and claims the benefit of foreign priority from the priorJapanese Patent Application No. 2014-035891, filed on Feb. 26, 2014,both applications are incorporated by reference in their entirety.

FIELD

The present invention relates to a technology for mounting asemiconductor device, and specifically to a heat releasing mechanismthat releases heat generated in a power device in the semiconductordevice.

BACKGROUND

Recently, in order to realize higher performance of automobiles, a powerdevice is used as one of semiconductor devices that support electronicsfor automobiles. A power device controls electric power for electronicsfor automobiles, and is used in various components including, forexample, hydraulic valve controllers of ABS's (Antilock Brake Systems)or the like, motor controllers of power windows or the like, invertersthat convert DC voltages of batteries or driving motors into DCvoltages, and the like.

Current main-stream power devices use silicon (Si) semiconductors. Alongwith the development of hybrid vehicles and electric vehicles,next-generation power devices which consume less power and are operableunder high-temperature and high-voltage conditions are now desired. Suchnew-generation power devices use, for example, silicon carbide (SiC),gallium nitride (GaN) or the like as described in, for example, JapanesePatent Application No. 2004-340918. These next-generation power deviceshave an operating frequency at the time of switching that is higher thanthat of conventional power devices. Therefore, when such anext-generation power device is mounted by a conventional method of wirebonding, there occurs a problem that electric noise is caused by aninductance component in the wire bonding part. In a worst case, theelectric noise destroys the power device itself.

A power device, especially, a power device for electronics forautomobiles is often used in an engine room, which may have a very hightemperature in certain environments of use. In addition, the powerdevice generates heat itself when being driven and thus has a very hightemperature. As a result, the temperature of the power device maypossibly be raised to 200° C. to 250° C. Such a high temperature of thepower device influences the switching characteristics thereof, and alsodeforms a resin material that is used to form the power device. Forthese reasons, the next-generation power device is desired to have ahigh heat releasing characteristic. In addition, the power device isused in a limited space such as an engine room or the like, andtherefore is required to be reduced in size.

SUMMARY

A semiconductor device in an embodiment according to the presentinvention includes a lead frame; a circuit board located on the leadframe; a power device including a switching element, the power devicebeing mounted on the circuit board via a bump located between the powerdevice and the circuit board; and a heat releasing member connected tothe power device.

The circuit board may be a multi-layer wiring board.

The circuit board may include a capacitor element, a resistor element,an inductor element, a diode element and a switching element.

The circuit board may include a circuit outputting an output signal inresponse to an input signal, the output signal being different from theinput signal.

The heat releasing member may be connected to the lead frame.

The semiconductor device may further include a sealing resin coveringthe lead frame, the circuit board, the power device and the heatreleasing member.

The semiconductor device may further include a sealing resin coveringthe lead frame, the circuit board, the power device and the heatreleasing member so as to expose a part of the heat releasing member. Asurface of the exposed part of the heat releasing member may be flushwith a surface of the sealing resin.

The semiconductor device may further include a sealing resin coveringthe lead frame, the circuit board, the power device and the heatreleasing member so as to expose a part of the heat releasing member. Atop surface and a side surface of the part of the heat releasing membermay be exposed.

The surface of the exposed part of the heat releasing member may have aconvexed and concaved shape.

The exposed part of the heat releasing member may include a flow pathformed therein.

The sealing resin may include a first resin and a second resin; thefirst resin may be located between the circuit board and the powerdevice; and the second resin may be located so as to cover the firstresin.

The first resin may have a coefficient of thermal expansion closer tothe coefficient of thermal expansion of the bump than the coefficient ofthermal expansion of the second resin.

The first resin may have a heat conductivity higher than the heatconductivity of the second resin.

The heat releasing member may extend in a plurality of differentdirections from the power device, and parts of the heat releasing memberextending in the plurality of different directions may be connected tothe lead frame.

The heat releasing member may cover at least circuits provided on thecircuit board.

The present invention provides a semiconductor device including ahigh-output power device that has a high heat releasing characteristic.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic plan view of a semiconductor device in Embodiment1 according to the present invention;

FIG. 2 is a cross-sectional view of the semiconductor device inEmbodiment 1 according to the present invention, taken along line A-B inFIG. 1;

FIG. 3 is a cross-sectional view of an example of horizontal switchingelement that may be included in a power device in the semiconductordevice in Embodiment 1 according to the present invention;

FIG. 4 is a cross-sectional view of an example of vertical switchingelement that may be included in the power device in the semiconductordevice in Embodiment 1 according to the present invention;

FIG. 5 is a cross-sectional view of a semiconductor device in amodification of Embodiment 1 according to the present invention, takenalong line A-B in FIG. 1;

FIG. 6 is a cross-sectional view showing a step in a method forproducing the semiconductor device in the modification of Embodiment 1according to the present invention, specifically, a step of mounting acircuit board on a lead frame;

FIG. 7 is a cross-sectional view showing a step in the method forproducing the semiconductor device in the modification of Embodiment 1according to the present invention, specifically, a step of mounting apower device on the circuit board by a flip-chip method;

FIG. 8 is a cross-sectional view showing a step in the method forproducing the semiconductor device in the modification of Embodiment 1according to the present invention, specifically, a step of forming anunder-fill resin between the circuit board and the power device;

FIG. 9 is a cross-sectional view showing a step in the method forproducing the semiconductor device in the modification of Embodiment 1according to the present invention, specifically, a step of forming ametal clip that connects the power device and the lead frame to eachother;

FIG. 10 is a cross-sectional view showing a step in the method forproducing the semiconductor device in the modification of Embodiment 1according to the present invention, specifically, a step of forming asecond resin;

FIG. 11 is a cross-sectional view of a semiconductor device inEmbodiment 2 according to the present invention, taken along line A-B inFIG. 1;

FIG. 12 is a cross-sectional view showing a step in a method forproducing the semiconductor device in Embodiment 2 according to thepresent invention, specifically, a step of setting a molding die for asecond resin and also setting a release film;

FIG. 13 is a cross-sectional view showing a step in the method forproducing the semiconductor device in Embodiment 2 according to thepresent invention, specifically, a step of filling a space in themolding die with the second resin;

FIG. 14 is a cross-sectional view showing a step in the method forproducing the semiconductor device in Embodiment 2 according to thepresent invention, specifically, a step of peeling off the release film;

FIG. 15 is a cross-sectional view of a semiconductor device inEmbodiment 3 according to the present invention, taken along line A-B inFIG. 1;

FIG. 16 is a cross-sectional view of a semiconductor device inmodification 1 of Embodiment 3 according to the present invention, takenalong line A-B in FIG. 1;

FIG. 17 is a cross-sectional view of a semiconductor device inmodification 2 of Embodiment 3 according to the present invention, takenalong line A-B in FIG. 1;

FIG. 18 is a cross-sectional view of a semiconductor device inmodification 3 of Embodiment 3 according to the present invention, takenalong line A-B in FIG. 1;

FIG. 19 is a cross-sectional view of a semiconductor device inmodification 4 of Embodiment 3 according to the present invention, takenalong line A-B in FIG. 1;

FIG. 20 is a schematic plan view of a semiconductor device in Embodiment4 according to the present invention;

FIG. 21 is a cross-sectional view of the semiconductor device inEmbodiment 4 according to the present invention, taken along line C-D inFIG. 20;

FIG. 22 is a schematic plan view of a semiconductor device inmodification 1 of Embodiment 4 according to the present invention;

FIG. 23 is a schematic plan view of a semiconductor device inmodification 2 of Embodiment 4 according to the present invention;

FIG. 24 is a schematic plan view of a semiconductor device in Embodiment5 according to the present invention; and

FIG. 25 is a cross-sectional view of the semiconductor device inEmbodiment 5 according to the present invention, taken along line E-F inFIG. 24.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a semiconductor device according to the present inventionwill be described with reference to the drawings. It should be notedthat the semiconductor device according to the present invention may becarried out in many different embodiments, and should not be construedas being limited to the following embodiments. In the drawings referredto in the following embodiments, the same components or componentshaving substantially the same functions will bear the same referencesigns, and descriptions thereof will not be repeated.

Embodiment 1

A semiconductor device 100 in Embodiment 1 according to the presentinvention will be described in detail with reference to FIG. 1 and FIG.2. FIG. 1 is a schematic plan view of the semiconductor device 100 inEmbodiment 1 according to the present invention. FIG. 2 is across-sectional view of the semiconductor device 100 in Embodiment 1according to the present invention, taken along line A-B in FIG. 1.

As shown in FIG. 1, the semiconductor device 100 in Embodiment 1includes a lead frame 110, a circuit board 120 located on the lead frame110, a power device 130 that includes a switching element and is mountedon the circuit board 120 via a bump located between the power device 130and the circuit board 120, a heat releasing member 140 that is formed ofa metal material and is connected to the power device 130, an integratedpassive device (IPD) 160 and a peripheral integrated circuit (IC) 165.

The power device 130 includes a three-terminal field effect transistor(FET) as the switching element. The three terminals of the field effecttransistor are respectively referred to as a source terminal, a drainterminal and a gate terminal. The FET operates as follows. In a statewhere a voltage is applied between a source electrode connected to thesource terminal and a drain electrode connected to the drain terminal, avoltage is applied to a gate electrode connected to the gate terminal.When this occurs, a channel is formed between the source electrode andthe drain electrode, and an electric current flows. The source terminalof the FET is connected to an external source terminal 112 via a wire ofthe circuit board 120 and also via the lead frame 110. The drainterminal of the FET is connected to a drain terminal pad 122 that islocated on the circuit board 120 via a wire of the circuit board 120.The drain terminal pad 122 is connected to an external drain terminal114 via a wire 123. The gate terminal of the FET is connected to a gateterminal pad 124 located on the circuit board 120 via a wire of thecircuit board 120. The gate terminal pad 124 is connected to an externalgate terminal 116 via a wire 125.

The lead frame 110 may be formed of a material having a high electricconductivity and a high heat release characteristic. The lead frame 110may be formed of, for example, a Cu material (C1020) or the like.

The circuit board 120 includes a circuit that transmits voltagessupplied from at least the external source terminal 112, the externaldrain terminal 114 and the external gate terminal 116 to the sourceterminal, the drain terminal and the gate terminal of the FET of thepower device 130. The circuit board 120 may be a multi-layer wiringboard. The circuit board 120 may be an organic printed wiring board(PWB), a ceramic direct copper bond (DCB) board, a metal base wiringboard using copper (Cu), aluminum (Al) or the like, acomponents-embedded board having a chip capacitor, a chip resistor andthe like embedded therein, or the like. The circuit board 120 may merelyinclude wires, or may be a functional circuit board that includes acapacitor element, a resistor element, an inductor element, a diodeelement and a switching element and outputs an output signal differentfrom an input signal when receiving the input signal.

The power device 130 is a semiconductor device capable of controllinghigh power of several hundred volts to several thousand volts. The powerdevice 130 may be a semiconductor device having switchingcharacteristics that are not easily changed in accordance with thetemperature. For a power device mounted on an automobile, a householdelectric/electronic appliance or the like, a switching element using,for example, a silicon (Si) substrate, a silicon carbide (SiC)substrate, a gallium nitride (GaN) substrate or the like is usable. Theswitching element may be a MOSFET (Metal Oxide Semiconductor FET), anIGBT (Insulated Gate Bipolar Transistor), a triac, a thyristor, a diode,an HEMT (High Electron Mobility Transistor) or the like.

The heat releasing member 140 may be formed of a metal material having ahigh heat conductivity and may be, for example, a copper plate. A heatreleasing member formed of a copper plate may be referred to as a “metalclip” or a “copper clip”. Alternatively, the heat releasing member 140may be a graphite sheet formed of graphite, which has a higher electricconductivity than that of copper. “Graphite” is a crystal in whichcarbon atoms arrayed in a hexagonal shape to have a mesh planarstructure are stacked in layers. A “graphite sheet” is obtained byprocessing the graphite into a sheet. A graphite sheet has aplanar-direction heat conductivity that is about four times that ofcopper, and provides high performance as a heat releasing member.

The IPD 160 is a circuit board in which a capacitor element, a resistorelement, an inductor element, a diode element and a switching elementare integrated together. The IPD 160 may include an antenna for wirelesscommunication with an external wireless device. The IPD 160 may belocated on the circuit board 120 as a separate component as shown inFIG. 1 or may be embedded in a components-embedded board as describedabove. The peripheral IC 165 is an LSI that controls the power device130, and controls the switching element included in the power device 130to be on or off.

As shown in FIG. 2, the lead frame 110 and the circuit board 120 areconnected to each other via an electrically conductive adhesive member118. The circuit board 120 and the power device 130 are connected toeach other via conductive bumps 128. The power device 130 is bonded by aso-called flip-chip method, by which the power device 130 in a face-downstate is connected to the circuit board 120. The power device 130 andthe heat releasing member 140 are connected to each other via a highlyheat conductive adhesive member 138, and the lead frame 110 and the heatreleasing member 140 are connected to each other via a highly heatconductive adhesive member 139. In this embodiment, the lead frame 110,the circuit board 120, the power device 130 and the heat releasingmember 140 are connected via the adhesive members or the bumps asdescribed above. Alternatively, these components may be connecteddirectly. For example, the lead frame 110 and the heat releasing member140 may be connected to each other directly.

The electrically conductive adhesive member 118 may be formed of solder,sintered silver (Ag) or the like. The bumps 128 may be formed of copper,silver, gold, solder or the like. The highly heat conductive adhesivemembers 138 and 139 may each be formed of an electrically conductiveadhesive material or an insulating adhesive material. The electricallyconductive adhesive material may be solder or the like. The insulatingadhesive material may be, for example, an organic adhesive materialcontaining an insulating ceramic filler, for example, alumina or thelike. The highly heat conductive adhesive members 138 and 139 need tohave a high heat conductivity, but may or may not need to have anelectric conductivity depending on the type of the switching element ofthe power device 130. As described in detail later, in the case where,for example, a vertical transistor is used as the switching element,namely, in the case where the power device 130 needs to be conductive ona rear surface thereof (surface directed in the direction of D1 in FIG.2), the highly heat conductive adhesive members 138 and 139 need to beformed of an electrically conductive material such as solder or thelike.

A sealing resin 150 is provided so as to cover the lead frame 110, thecircuit board 120, the power device 130 and the heat releasing member140. The sealing resin 150 secures the above-listed components, preventsthe above-listed components from being contaminated with moisture orimpurities from outside, and alleviates impact from outside to protectthe above-listed components. The sealing resin 150 may be formed of anepoxy resin, a cyanate ester resin, an acrylic resin, a polyimide resin,a silicone resin or the like.

Now, the switching element of the power device 130 will be describedwith reference to FIG. 3 and FIG. 4. FIG. 3 is a cross-sectional view ofan example of horizontal switching element 200 that may be included inthe power device 130 in the semiconductor device 100 in Embodiment 1according to the present invention. FIG. 4 is a cross-sectional view ofan example of vertical switching element 300 that may be included in thepower device 130 in the semiconductor device 100 in Embodiment 1according to the present invention.

The horizontal switching element 200 shown in FIG. 3 is also referred toas a “planar-type transistor” and may be, for example, an Si-substrateMOSFET, a GaN-substrate MOSFET, a GaN-substrate HEMT or the like. Astructure of the horizontal switching element 200 will be brieflydescribed with reference to FIG. 3. The horizontal switching element 200includes a semiconductor substrate 210, a source electrode 220, a drainelectrode 230, a gate insulating film 240 and a gate electrode 250. Thesemiconductor substrate 210 and the gate electrode 250 are insulatedfrom each other by the gate insulating film 240.

The horizontal switching element 200 operates as follows. A voltage isapplied to the gate electrode 250. An electric field generated by thevoltage application allows electrons to be gathered to an area of thesemiconductor substrate 210 that is close to the gate insulating film240. As a result, a channel is formed to turn on the switching element200. When a voltage is applied between the source electrode 220 and thedrain electrode 230 in this state, an electric field generated by thevoltage application allows the electrons to be transferred horizontally.As a result, an electric current flows. As can be seen, in thehorizontal switching element 200, the source electrode 220, the drainelectrode 230 and the gate electrode 250 are respectively connected to asource terminal 221, a drain terminal 231 and a gate terminal 251 at asurface directed oppositely to the direction of D1 (at a top surface ofeach electrode). Namely, the three terminals used to drive thetransistor are all located on the side of a top surface of the powerdevice 130.

The vertical switching element 300 shown in FIG. 4 may be, for example,an SiC-substrate MOSFET or the like. A structure of the verticalswitching element 300 will be briefly described with reference to FIG.4. The vertical switching element 300 includes an N-type epitaxialgrowth layer 310, a P-type implanted layer 320, an N-type implantedlayer (also referred to as a “source electrode”) 325, an N-type SiCsubstrate (also referred to as a “drain electrode”) 330, a gateinsulating layer 340 and a gate electrode 350. The N-type epitaxialgrowth layer 310 and the gate electrode 350 are insulated from eachother by the gate insulating film 340. At an interface between theN-type implanted layer 325 and the P-type implanted layer 320, a p-njunction is formed.

In the vertical switching element 300, the p-n junction is formed at theinterface between the N-type implanted layer 325 and the P-typeimplanted layer 320. Therefore, in a state where no voltage is appliedto the gate electrode 350, no electric current flows from the N-typeimplanted layer 325 to the P-type implanted layer 320. By contrast, in astate where a voltage is applied to the gate electrode 350, the energybarrier of the p-n junction is lowered to provide a state where anelectric current flows from the N-type implanted layer 325 to the P-typeimplanted layer 320 (a state where the switching element 300 is on).When a voltage is applied between the N-type implanted layer 325 and theN-type SiC substrate 330 in this state, an electric field generated bythe voltage application allows electrons to be transferred vertically.As a result, an electric current flows. As can be seen, in the verticalswitching element 300, the source electrode 325 and the gate electrode350 are respectively connected to a source terminal 321 and a gateterminal 351 at a surface directed oppositely to the direction of D1 (ata top surface of each electrode). The drain electrode 330 is connectedto a drain terminal 331 at a surface directed in the direction of D1 (ata rear surface thereof). Namely, the three terminals used to drive thetransistor are located on the side of a top surface and a rear surfaceof the power device 130.

As described above, in the semiconductor device 100 in Embodiment 1, therear surface of the power device 130 and the lead frame 110 areconnected to each other via the heat releasing member 140. Therefore,heat generated by the driving of the switching element included in thepower device 130 is transmitted to the lead frame 110 efficiently viathe heat releasing member 140. Thus, a high heat releasingcharacteristic is provided by the power device 130, which has a highoutput. In addition, the power device 130 is connected to the circuitboard 120 via the bumps 128 by the flip-chip method. Therefore, theinductor component in the connection part is smaller than in the casewhere the power device 130 is connected to the circuit board 120 by awire bonding method. This suppresses electric noise from being caused inthe connection part. Since the power device 130 is mounted on the leadframe 110 via the circuit board 120, components having functionsrequired for the semiconductor device 100 are allowed to be stacked.Therefore, the semiconductor device 100 is reduced in size.

(Modification of Embodiment 1)

With reference to FIG. 5 through FIG. 10, a semiconductor device 100 ina modification of Embodiment 1 according to the present invention willbe described in detail. First, with reference to FIG. 5, a structure ofthe semiconductor device 100 in the modification of Embodiment 1 will bedescribed. Then, with reference to FIG. 6 through FIG. 10, a method forproducing the semiconductor device 100 in the modification of Embodiment1 will be described. A plan view of the semiconductor device 100 in themodification of Embodiment 1 is substantially the same as that in FIG.1, and thus FIG. 1 is used as a plan view of the semiconductor device100 in the modification of Embodiment 1.

FIG. 5 is a cross-sectional view of the semiconductor device 100 inEmbodiment 1 according to the present invention, taken along line A-B inFIG. 1. FIG. 5 is similar to FIG. 2, but is different from FIG. 2 in thefollowing point. In FIG. 5, the semiconductor device 100 includes afirst resin 170 provided between the circuit board 120 and the powerdevice 130, and a second resin 180 located so as to cover the firstresin 170. The first resin 170 is provided to secure the circuit board120 and the power device 130 to each other, and is also referred to asan “under-fill resin”. The second resin 180 is formed of the samematerial as that of the sealing resin 150 shown in FIG. 2.

The first resin 170 may have a coefficient of thermal expansion that iscloser to that of the bumps 128 than that of the second resin 180. Thefirst resin 170 may have a heat conductivity that is higher than that ofthe second resin 180. The first resin 170 may be formed of an epoxyresin, a cyanate ester resin, an acrylic resin, a polyimide resin, asilicone resin or the like, like the sealing resin 150 shown in FIG. 2.Alternatively, the first resin 170 may be formed of a resin materialthat contains impurities and thus is adjusted to have theabove-described coefficient of thermal expansion or heat conductivity.The first resin 170 may be formed of, for example, an epoxy resincontaining silica filler.

As described above, in the semiconductor device 100 in the modificationof Embodiment 1, the first resin 170 is provided between the circuitboard 120 and the power device 130, which are connected to each othervia the bumps 128. This further improves the connection strength betweenthe circuit board 120 and the power device 130. Therefore, themechanical strength of the semiconductor device 100 is increased. If,for example, in the structure shown in FIG. 2, the difference betweenthe coefficient of thermal expansion of the bumps 128 and that of thesealing resin 150 is large, the bumps 128 may possibly be peeled offfrom the circuit board 120 or the power device 130 by a stress caused bythermal expansion and contraction, and as a result, the electricconnection between the circuit board 120 and the power device 130 maypossibly be broken.

However, in the modification of Embodiment 1, the coefficient of thermalexpansion of the first resin 170 is closer to that of the bumps 128 thanthat of the second resin 180. This alleviates the stress caused to thebumps 128 by the thermal expansion and contraction. Therefore, the bumps128 are suppressed from being peeled off from the circuit board 120 orthe power device 130. In addition, the heat conductivity of the firstresin 170 is higher than that of the second resin 180. This allows theheat generated in the power device 130 to be transmitted easily to thelead frame 110 via the circuit board 120. Therefore, a high heatreleasing characteristic is provided by the power device 130, which hasa high output.

Now, a method for producing the semiconductor device 100 shown in FIG. 5will be described with reference to cross-sectional views. FIG. 6 is across-sectional view showing a step in the method for producing thesemiconductor device 100 in the modification of Embodiment 1 accordingto the present invention, specifically, a step of mounting the circuitboard 120 on the lead frame 110. First, melted solder is dripped ontothe lead frame 110, and the circuit board 120 is attached to the leadframe 110 before the solder is solidified. The circuit board 120 isattached to the lead frame 110 while being aligned such that an externalterminal of the circuit board 120 contacts the solder. According to analternative method that does not use the solder, a solvent containingnano-sized silver particles dispersed therein is applied to the leadframe 110, the circuit board 120 is attached to the lead frame 110, andthe assembly of the lead frame 110 and the circuit board 120 isheat-treated to be solidified (sintered).

FIG. 7 is a cross-sectional view showing a step in the method forproducing the semiconductor device 100 in the modification of Embodiment1 according to the present invention, specifically, a step of mountingthe power device 130 on the circuit board 120 by the flip-chip method.In the step shown in FIG. 7, the bumps 128 are formed on the powerdevice 130 in correspondence with an input part (not shown) located onthe top surface of the power device 130, and the power device 130 isattached to the circuit board 120 in a face-down state, namely, in astate where the top surface of the power device 130 faces a surface ofthe circuit board 120. The power device 130 is attached to the circuitboard 120 while being aligned such that an output part of the circuitboard 120 contacts the bumps 128. According to an alternative method,the bumps 128 are formed on the surface of the circuit board 120, andthen the power device 130 is attached to the circuit board 120.

FIG. 8 is a cross-sectional view showing a step in the method forproducing the semiconductor device 100 in the modification of Embodiment1 according to the present invention, specifically, a step of formingthe under-fill resin 170 between the circuit board 120 and the powerdevice 130. In the step shown in FIG. 8, the first resin 170 is formedas the under-fill resin between the circuit board 120 and the powerdevice 130, which are connected to each other via the bumps 128. Thefirst resin 170 may be injected in one direction so that no gap isformed between the circuit board 120 and the power device 130. This willbe described more specifically. In a state where the lead frame 110having the circuit board 120 and the power device 130 mounted thereon asshown in FIG. 7 is heated, the first resin 170 is dripped onto an areaof the circuit board 120 that is close to an end of the power device130. The dripped first resin 170 spreads between the circuit board 120and the power device 130 because of a capillary action. Since thesurface of the circuit board 120 is heated, the viscosity of the firstresin 170 is decreased. Thus, the first resin 170 spreads between thecircuit board 120 and the power device 130 more smoothly than in thecase where the surface of the circuit board 120 is not heated.

In the process described above with reference to FIG. 7 and FIG. 8, thepower device 130 is mounted on the circuit board 120 via the bumps 128,and then the first resin 170 is formed. The present invention is notlimited to this process. According to an alternative method, the firstresin 170 is applied to the circuit board 120, and then the power device130 having the bumps 128 formed thereon is mounted on the circuit board120 by a thermal press bonding method. According to another alternativemethod, the bumps 128 are formed on the circuit board 120, then thefirst resin 170 is applied thereto, and the power device 130 is mountedon the circuit board 120 by the thermal press bonding method.

FIG. 9 is a cross-sectional view showing a step in the method forproducing the semiconductor device 100 in the modification of Embodiment1 according to the present invention, specifically, a step of formingthe metal clip 140 that connects the power device 130 and the lead frame110 to each other. In the step shown in FIG. 9, the highly heatconductive adhesive members 138 and 139 formed of solder are drippedonto the rear surface of the power device 130 and onto the lead frame110 respectively. Before the solder is solidified, the heat releasingmember 140 is mounted on the power device 130 and the lead frame 110.

FIG. 10 is a cross-sectional view showing a step in the method forproducing the semiconductor device 100 in the modification of Embodiment1 according to the present invention, specifically, a step of formingthe second resin 180. In the step shown in FIG. 10, the lead frame 110having the circuit board 120, the power device 130 and the heatreleasing member 140 formed thereon is placed in a molding die 181, anda resin material is injected into the molding die 181. Thus, the secondresin 180 is formed. In the process shown in FIG. 10, the second resin180 is formed by use of the molding die 181. The present invention isnot limited to this process. According to an alternative method, thesecond resin 180 is formed by, for example, applying the resin materialonce or a plurality of times with no use of any molding die.

As described above, in the method for producing the semiconductor device100 in the modification of Embodiment 1, the first resin 170 is formedbetween the circuit board 120 and the power device 130 before the heatreleasing member 140 is formed. This suppresses the circuit board 120and the power device 130 from being displaced from each other at thetime of mounting the heat releasing member 140. Therefore, the processis more stable, and the semiconductor device 100 produced by this methodhas a high reliability without insufficient electric conductance due toan alignment error.

Embodiment 2

A semiconductor device 100 in Embodiment 2 according to the presentinvention will be described in detail with reference to FIG. 11 throughFIG. 14. First, with reference to FIG. 11, a structure of thesemiconductor device 100 in Embodiment 2 will be described. Then, withreference to FIG. 12 through FIG. 14, a method for producing thesemiconductor device 100 in Embodiment 2 will be described. A plan viewof the semiconductor device 100 in Embodiment 2 is substantially thesame as that in FIG. 1, and thus FIG. 1 is used as a plan view of thesemiconductor device 100 in Embodiment 2.

FIG. 11 is a cross-sectional view of the semiconductor device 100 inEmbodiment 2 according to the present invention, taken along line A-B inFIG. 1. FIG. 11 is similar to FIG. 5, but is different from FIG. 5 inthe following point. In FIG. 11, a surface 141 of a part of the heatreleasing member 140 is exposed from the second resin 180. Namely, thesecond resin 180 covers the lead frame 110, the circuit board 120, thepower device 130 and the heat releasing member 140 so as to expose apart of the heat releasing member 140. The surface 141 of the exposedpart of the heat releasing member 140 may be flush with a surface of thesecond resin 180.

As described above, in the semiconductor device 100 in Embodiment 2, apart of the heat releasing member 140 is exposed. Therefore, heatgenerated in the power device 130 is released outside through theexposed part of the heat releasing member 140. Thus, a high heatreleasing characteristic is provided by the power device 130, which hasa high output. Specifically, in actual use of the semiconductor device100 including the power device 130, a cooling mechanism is occasionallyprovided on a surface of the semiconductor device 100 directed in thedirection of D1. In this case, the exposed part of the heat releasingmember 140 is made closer to the cooling mechanism, and therefore, ahigher heat releasing effect is provided than in the case where the heatreleasing member 140 is not exposed. The surface 141 of the exposed partof the heat releasing member 140 and the surface of the second resin 180are flush with each other. Therefore, in the case where the coolingmechanism is in contact with the surface of the semiconductor device 100directed in the direction of D1, the cooling mechanism is suppressedfrom contacting the semiconductor device 100 unstably (loosely). Thus,the contact between the semiconductor device 100 and the coolingmechanism of an external device is stabilized.

Now, a method for producing the semiconductor device 100 shown in FIG.11 will be described with reference to cross-sectional views. FIG. 12 isa cross-sectional view showing a step in the method for producing thesemiconductor device 100 in Embodiment 2 according to the presentinvention, specifically, a step of setting a molding die 182 for thesecond resin and also setting a release film 184. In the step shown inFIG. 12, the lead frame 110 having the circuit board 120, the powerdevice 130 and the heat releasing member 140 mounted thereon is placedin the molding die 182 having an opening 183. On the molding die 182,the release film 184 is placed so as to contact the surface 141 of theexposed part of the heat releasing member 140. A surface of the releasefilm 184 (surface to be in contact with the second resin 180) may becoated with an organic film in order to suppress the second resin 180from being bonded with the release film 184. The organic film may beformed of a polytetrafluoroethylene resin, a silicone resin, a fluorineresin or the like.

FIG. 13 is a cross-sectional view showing a step in the method forproducing the semiconductor device 100 in Embodiment 2 according to thepresent invention, specifically, a step of filling a space in themolding die 182 with the second resin 180. In the step shown in FIG. 13,a resin material is injected into the molding resin 182 through theopening 183 to form the second resin 180. One or both of the molding die182 and the release film 184 may have an ventilation opening so that airis not confined to generate air bubbles or the like in this step. Theventilation opening may be provided on the side opposite to the opening183. The surface 141 of the exposed part of the heat releasing member140 may be bonded with the release film 184 so that the second resin 180is not formed on the surface 141 of the exposed part of the heatreleasing member 140.

FIG. 14 is a cross-sectional view showing a step in the method forproducing the semiconductor device 100 in Embodiment 2 according to thepresent invention, specifically, a step of peeling off the release film184. In the step shown in FIG. 14, the release film 184 is peeled offafter the space in the molding die 182 is filled with the second resin180. The release film 184 may be peeled off before or after the secondresin 184 is cured. The release film 184 is easily peeled off because ofthe organic film coating the surface of the release film 184.

In the step shown in FIG. 14, the release film 184 is peeled off, andthen the semiconductor device 100 is removed from the molding die 182.Thus, the semiconductor device 100 shown in FIG. 11 is obtained.

There may be a case where the second resin 180 is formed also on thesurface 141 of the exposed part of the heat releasing member 140. Inorder to allow the surface 141 of the exposed part of the heat releasingmember 140 to be exposed from the second resin 180 with certainty, themethod for producing the semiconductor device 100 may further include astep of exposing the surface 141 of the exposed part of the heatreleasing member 140 after the second resin 180 is formed. For example,the thickness of the second resin 180 may be decreased by dry etching,O₂ plasma treatment or the like. Alternatively, both of the second resin180 and the heat releasing member 140 may be polished by mechanicalpolishing, chemical mechanical polishing (CMP) or the like.

As described above, in the method for producing the semiconductor device100 in Embodiment 2, the second resin 180 is formed by use of themolding die 182 and the release film 184. In this manner, the secondresin 180 exposing a part of the heat releasing member 140 is easilyformed. Therefore, the semiconductor device 100 shown in FIG. 11 isproduced at low cost by a relatively simple process.

Embodiment 3

An overview of a semiconductor device 100 in Embodiment 3 according tothe present invention will be described in detail with reference to FIG.15. A plan view of the semiconductor device 100 in Embodiment 3 issubstantially the same as that in FIG. 1, and thus FIG. 1 is used as aplan view of the semiconductor device 100 in Embodiment 3. FIG. 15 is across-sectional view of the semiconductor device 100 in Embodiment 3according to the present invention, taken along line A-B in FIG. 1. FIG.15 is similar to FIG. 11, but is different from FIG. 11 in the followingpoint. In FIG. 15, an exposed part of the heat releasing member 140protrudes from the second resin 180. Namely, the second resin 180 coversthe lead frame 110, the circuit board 120, the power device 130 and theheat releasing member 140 such that a part of the heat releasing member140 protrudes from the second resin 180; and a top surface and a sidesurface of the part of the heat releasing member 140 are exposed.

In FIG. 15, it is preferable that the protruding part of the heatreleasing member 140 has a thickness that is at least ¼ of the totalthickness of the heat releasing member 140. More preferably, theprotruding part of the heat releasing member 140 has a thickness that isat least ½ of the total thickness of the heat releasing member 140.

The semiconductor device 100 shown in FIG. 15 is obtained by selectivelyremoving a part of the second resin 180 from the semiconductor device100 shown in FIG. 11. The second resin 180 may be partially removed by,for example, dry etching, by which the difference between the etchingrate of the heat releasing member 140 and that of the second resin 180is large, or by plasma treatment.

As described above, in the semiconductor device 100 in Embodiment 3, apart of the heat releasing member 140 is exposed. Therefore, heatgenerated in the power device 130 is released outside through theexposed part of the heat releasing member 140. Since an area size of thesurface of the exposed part of the heat releasing member 140 is larger,a higher heat releasing characteristic is provided. In addition, theexposed part of the heat releasing member 140 protrudes. When thesemiconductor device 100 in Embodiment 3 is water-cooled or air-cooled,convection of water or air is easily caused in the vicinity of theprotruding part because of this structure. This provides a highercooling effect than in the case where the exposed part of the heatreleasing member 140 does not protrude.

(Modifications of Embodiment 3)

With reference to FIG. 16 through FIG. 19, overviews of semiconductordevices in modifications of Embodiment 3 will be described in detail.FIG. 1 is used as a plan view of the semiconductor device in each of themodifications 1, 2, 3 and 4 of Embodiment 3. FIG. 16 is across-sectional view of the semiconductor device in modification 1 ofEmbodiment 3 according to the present invention, taken along line A-B inFIG. 1. FIG. 17 is a cross-sectional view of the semiconductor device inmodification 2 of Embodiment 3 according to the present invention, takenalong line A-B in FIG. 1. FIG. 18 is a cross-sectional view of thesemiconductor device in modification 3 of Embodiment 3 according to thepresent invention, taken along line A-B in FIG. 1. FIG. 19 is across-sectional view of the semiconductor device in modification 4 ofEmbodiment 3 according to the present invention, taken along line A-B inFIG. 1.

In modification 1 shown in FIG. 16, a surface 141 of the exposed part ofthe heat releasing member 140 is roughened (also referred to as“stain-finished”). The roughened surface of the heat releasing member140 shown in FIG. 16 may be obtained by roughening the surface of theexposed part of the heat releasing member 140 in the semiconductordevice 100 shown in FIG. 15 by a blasting method or a polishing methodusing a file. Alternatively, the heat releasing member 140 may be formedby use of a material having a surface that is entirely or partiallyrough. In modification 2 shown in FIG. 17, a surface 141 of the exposedpart of the heat releasing member 140 has a pattern (also referred to as“microscopic shapes” or “texture”). The pattern may be obtained byprocessing the surface of the exposed part of the heat releasing member140 in the semiconductor device 100 shown in FIG. 15 by aphotolithography process or an etching process. Alternatively, the heatreleasing member 140 may be formed by use of a material having apattern.

The state of the surface 141 of the exposed part of the heat releasingmember 140 shown in each of FIG. 16 and FIG. 17 may be referred to as a“convexed and concaved shape”. Namely, the semiconductor device shown ineach of FIG. 16 and FIG. 17 may be expressed as having a convexed andconcaved shape at the surface 141 of the exposed part of the heatreleasing member 140. As can be seen, in modifications 1 and 2 ofEmbodiment 3, an area size of the surface of the exposed part of theheat releasing member 140 is made larger, which provides a higher heatreleasing characteristic.

In modification 3 shown in FIG. 18, a hollow flow path 145 is formed inthe heat leasing member 140. Cooling water or cooling gas (the gas maybe air) is caused to flow in the flow path 145, and thus the heatreleasing member 140 is cooled efficiently. The flow path 145 may beformed in the heat releasing member 140 in advance, or may be formed bybonding the heat releasing member 140 shown in FIG. 17 and another heatreleasing member.

In modification 4 shown in FIG. 19, the semiconductor device 100 inEmbodiment 3 according to the present invention is attached to anotherdevice. A flow path 146 of a pattern having a convexed and concavedshape is formed at the surface of the heat releasing member 140. In FIG.19, the flow path 146 is formed in an area enclosed by the heatreleasing member 140 and a component 190 of the another device. In thecase of modification 4 shown in FIG. 19, the surface of the exposed partof the heat releasing member 140 and the surface of the second resin 180may be flush with each other.

In the semiconductor device shown in each of FIG. 18 and FIG. 19, theflow path formed in the heat releasing member 140 allows cooling wateror cooling gas to flow therein, and thus actively cools the heatreleasing member 140. Therefore, a higher heat releasing characteristicis provided.

Embodiment 4

An overview of a semiconductor device 100 in Embodiment 4 according tothe present invention will be described in detail with reference to FIG.20 and FIG. 21. FIG. 20 is a schematic plan view of the semiconductordevice 100 in Embodiment 4 according to the present invention. FIG. 21is a cross-sectional view of the semiconductor device 100 in Embodiment4 according to the present invention, taken along line C-D in FIG. 20.

FIG. 20 is similar to FIG. 1, but is different from FIG. 1 in thefollowing point. In FIG. 20, the heat releasing member 140 extends intwo different directions from the power device 130, and parts of theheat releasing member 140 extending in the two different directions areconnected to the lead frame 110, respectively at a first connectionpoint 401 and a second connection point 402. As can be seen from thecross-sectional shape of the semiconductor device 100 shown in FIG. 21,the heat releasing member 140 connected to the rear surface of the powerdevice 130 is connected to the lead frame 110 at the first connectionpoint 401 and the second connection point 402.

As can be seen, in the semiconductor device 100 in Embodiment 4, heatgenerated in the power device 130 is transmitted to the lead frame 110via the heat releasing member 140 from the first connection point 401and the second connection point 402. Therefore, a higher heat releasingcharacteristic is provided.

(Modification 1 of Embodiment 4)

With reference to FIG. 22, an overview of a semiconductor device 100 inmodification 1 of Embodiment 4 according to the present invention willbe described in detail. FIG. 22 is a schematic plan view of thesemiconductor device 100 in modification 1 of Embodiment 4 according tothe present invention.

FIG. 22 is similar to FIG. 20, but is different from FIG. 20 in thefollowing point. In FIG. 22, the heat releasing member 140 extends inthree different directions from the power device 130, and parts of theheat releasing member 140 extending in the three different directionsare connected to the lead frame 110, respectively at a first connectionpoint 401, a second connection point 402 and a third connection point403.

As can be seen, in the semiconductor device 100 in modification 1 ofEmbodiment 4, heat generated in the power device 130 is transmitted tothe lead frame 110 via the heat releasing member 140 from the firstconnection point 401, the second connection point 402 and the thirdconnection point 403. Therefore, a higher heat releasing characteristicis provided.

(Modification 2 of Embodiment 4)

With reference to FIG. 23, an overview of a semiconductor device 100 inmodification 2 of Embodiment 4 according to the present invention willbe described in detail. FIG. 23 is a schematic plan view of thesemiconductor device 100 in modification 2 of Embodiment 4 according tothe present invention.

FIG. 23 is similar to FIG. 20, but is different from FIG. 20 in thefollowing point. In FIG. 23, the heat releasing member 140 is formed soas to cover the power device 130, the IPD 160 and the peripheral IC 165.In the structure shown in FIG. 23, the heat releasing member 140 coversthe entirety of all of the power device 130, the IPD 160 and theperipheral IC 165. The present invention is not limited to thisstructure. The present invention is applicable to a structure in whichthe heat releasing member 140 covers at least a part of a componenthaving characteristics that are changed by the influence ofelectromagnetic waves.

As can be seen, in the semiconductor device 100 in modification 2 ofEmbodiment 4, heat generated in the power device 130 is transmitted tothe lead frame 110 via the heat releasing member 140 from the firstconnection point 401 and the second connection point 402. Therefore, ahigher heat releasing characteristic is provided. In addition, the heatreleasing member 140 covers the power device 130, the IPD 160 and theperipheral IC 165, and therefore, suppresses the characteristics of thecircuits of these components from being changed by the influence ofexternal electromagnetic waves. Thus, the characteristics are stable andare not influenced by the environments.

Embodiment 5

An overview of a semiconductor device 100 in Embodiment 5 according tothe present invention will be described in detail with reference to FIG.24 and FIG. 25. FIG. 24 is a schematic plan view of the semiconductordevice 100 in Embodiment 5 according to the present invention. FIG. 25is a cross-sectional view of the semiconductor device 100 in Embodiment5 according to the present invention, taken along line E-F in FIG. 24.

FIG. 24 is similar to FIG. 1, but is different from FIG. 1 in thefollowing point. In FIG. 24, the heat releasing member 140 is locatedonly on the power device 130 and is not connected to the lead frame 110.In the structure shown in FIG. 24 and FIG. 25, the heat releasing member140 is located so as to cover the entirety of the power device 130. Thepresent invention is not limited to this structure. Alternatively, theheat releasing member 140 may cover only a part of the power device 130.Namely, in FIG. 24, there may be an area of the power device 130 that isnot covered with the heat releasing member 140. Still alternatively, asshown in FIG. 23, the heat releasing member 140 may be located to so asto cover the IPD 160 and the peripheral IC 165.

As can be seen, in the semiconductor device 100 in Embodiment 5, a highheat releasing characteristic is provided with a smaller heat releasingmember. This decreases the amount of material used for the heatreleasing member, and thus provides the effect of cost reduction.

The present invention is not limited to the above-described embodiments,and the embodiments may be optionally altered without departing from thegist of the present invention.

What is claimed is:
 1. A semiconductor device, comprising: a lead frame;a circuit board located on the lead frame; a power device including aswitching element, the power device being mounted on the circuit boardvia a bump located between the power device and the circuit board; aheat releasing member connected to the power device; and a sealing resincovering the lead frame, the circuit board, the power device and theheat releasing member so as to expose a part of the heat releasingmember, wherein a top surface and a side surface of the part of the heatreleasing member are exposed.
 2. The semiconductor device according toclaim 1, wherein the circuit board is a multi-layer wiring board.
 3. Thesemiconductor device according to claim 1, wherein the circuit boardincludes a capacitor element, a resistor element, an inductor element, adiode element and a switching element.
 4. The semiconductor deviceaccording to claim 1, wherein the circuit board includes a circuitoutputting an output signal in response to an input signal, the outputsignal being different from the input signal.
 5. The semiconductordevice according to claim 1, wherein the heat releasing member isconnected to the lead frame.
 6. The semiconductor device according toclaim 1, wherein the top surface of the exposed part of the heatreleasing member has a convexed and concaved shape.
 7. The semiconductordevice according to claim 1, wherein the exposed part of the heatreleasing member includes a flow path.
 8. The semiconductor deviceaccording to claim 1, wherein: the sealing resin includes a first resinand a second resin; the first resin is located between the circuit boardand the power device; and the second resin is located so as to cover thefirst resin.
 9. The semiconductor device according to claim 8, whereinthe first resin has a coefficient of thermal expansion closer to thecoefficient of thermal expansion of the bump than the coefficient ofthermal expansion of the second resin.
 10. The semiconductor deviceaccording to claim 8, wherein the first resin has a heat conductivityhigher than the heat conductivity of the second resin.
 11. Thesemiconductor device according to claim 6, wherein the convexed andconcaved shape is a roughened shape.
 12. The semiconductor deviceaccording to claim 6, wherein the convexed and concaved shape is astain-finished shape.
 13. The semiconductor device according to claim 6,wherein the convexed and concaved shape is a microscopic pattern. 14.The semiconductor device according to claim 6, wherein the convexed andconcaved shape is a texture pattern.
 15. The semiconductor deviceaccording to claim 7, wherein the flow path is formed in the heatreleasing member.